There are some known conventional in-wheel motor drives as seen in Japanese Unexamined Patent Application Publication Nos. 2009-52630 (PTL 1) and 2009-174593 (PTL 2). Each of the in-wheel motor drives disclosed in PTL 1 and PTL 2 has a drive motor, a speed reducer that receives a driving force from the drive motor and reduces rotational speed to output the reduced rotation to a wheel, and a wheel hub member coupled with an output shaft of the speed reducer, and the drive motor, speed reducer and wheel hub member are coaxially arranged in a line. The speed reducer adopts a cycloid reduction mechanism that provides a high speed reduction ratio in comparison with a general planetary gear speed reduction mechanism regarded as a conventional speed reducer. Such a configuration allows the torque required for the drive motor to be small and therefore the in-wheel motor drive to be advantageously reduced in size and weight.
In the manufacture and assembly of the in-wheel motor drives as disclosed in PTL 1 and PTL 2, an inner ring of a wheel hub bearing is fabricated by fixedly coupling a wheel hub and a wheel-side rotation member through a tube forming method. An exterior member, serving as an outer ring of the wheel hub bearing, is secured with bolts to one end face of a cylindrical speed-reduction-unit casing, serving as an outer circumferential surface of the speed reduction unit. Then, rotation members, two curved plates, inner pins, outer pins, and some other components are inserted in a predetermined order from an opening on the other end of the speed-reduction-unit casing to assemble the components one by one inside the speed reduction unit.
In the next assembly step, one end face of a cylindrical motor-unit casing is secured to the end face, in which the opening is formed, of the speed-reduction-unit casing. Since the motor unit disclosed in PTL 1 is an axial gap motor with stators on opposite sides of the motor unit in an axial direction, a stator for one side is first inserted, then a rotor is inserted, and a stator for the other side is inserted into the motor-unit casing from an opening formed on the other end thereof to assemble the components one by one inside the motor unit.
Since the motor unit in PTL 2 is a radial gap motor, components are inserted from an opening on an end of a motor-unit casing, separately, in a predetermined order and assembled one by one inside the motor unit. More specifically, after an end face of the motor-unit casing is secured to an end face of the speed-reduction-unit casing, a stator is first inserted from an opening on the other end of the motor-unit casing and then secured to an inner circumferential surface of the casing. Second, a rotor is inserted and the rotary shaft of the rotor is secured to an end of a rotation member projecting from the speed reduction unit.